Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $238.80   8.308%   $258.6395   $258.64   $258.65   $258.60  
  Purchase #2 $198.78   3.128%   $204.9978   $205.00   $205.00   $205.00  
  Purchase #3 $180.74   5.114%   $189.983   $189.98   $190.00   $190.00  
  Purchase #4 $88.97   4.814%   $93.253   $93.25   $93.25   $93.30  
  Purchase #5 $226.33   3.244%   $233.6721   $233.67   $233.65   $233.70  
  Purchase #6 $206.90   13.408%   $234.6412   $234.64   $234.65   $234.60  
  Purchase #7 $226.27   8.617%   $245.7677   $245.77   $245.75   $245.80  
  7 purchase totals = $1,366.79       $1,460.9543   $1,460.95   $1,460.95   $1,461.00